Its likely that Andros' duties in Space and Ashleu's home being Earth got in the way of their relationship. I think they were happy for a time. But decided to let each other go. Much like how Tommy and Kim ended. Without the Dear John Stuff.

They were both young. So its not like they necessarily were going to end up married. Ashley liked Carlos at one point. So things can change. Its not like Andros was really used to being in a relationship anyway.